The bracelet if my fitbit charge 2 is broken. how can i have a replacement one for free?

Yes, a Fitbit Charge 2 band can be replaced. There is a small lever on the underside of the band near the watch that allows you to pull the band off when pulled. Replacement bands can be bought online or in stores. Be sure to buy bands for Fitbit Charge 2 only.

The battery is very small and it could be easily over charged. If that is the case, it will show charged and it wont work. You cannot replace the battery yourself.

Sorry, but We do not supply parts. This is an repairs advice website. I would suggest you go to another store that sells Fitbits to buy a replacement. You could also go directly to Fitbit to see if they can supply you with one. I do not understand why BestBuy referred you here. They must not supply replacement parts so we're possibly referring you to another more specialist store.

Of course you can do it with a screen protector.
The Guide Of Reset Fitbit Charge HR Complete Guide

Contact.fitbit.com You will also find thos info in the warranty, this can be found at the bottom of any page on fitbit